This has been going on for quite some time, probably years even since I've used SeaMonkey way back when it was launched as Mozilla. SeaMonkey on OSX has gotten very slow/sluggish basically doing everything. This hasn't been an out of nowhere thing, just progressively more noticeable as time as gone on especially me using Chrome much more because of the aforementioned and just feeling how everything is more speedy. Along with that, I regularly perform maint on OSX and keep an eye on console messages and Diagnostic Reports. Seamonkey the past few years has been very bad at filling out the System Diagnostic Report section with various wakeups_resource and cpu_resource messages. Normally I'd go in there after a number of months and begrudgingly delete them out, but it's finally got to the point where I feel this needs to be reported and sharing the logs in the hopes either something can be discovered and fixed/optimized in future versions, or I can find the culprit if it's my computer. I'm not experiencing this issue with any other programs, particularly testing with Chrome, FireFox, or Safari.

Here's a pic of just a sample of what normally builds up over time with SeaMonkey: